Control method for a cryogenic unit

Abstract

Apparatus and methods for improving efficiency of a temperature conditioning system which employs a cryogenic liquid. A vapor powered ventilation motor is normally powered by vapor from the low pressure end of the evaporation coils. However, supplemental vapor is provided at start-up to provide immediate ventilation. In addition, vapor which bleeds off valves is cycled through the vapor powered motor or used to maintain a slight positive pressure when the system is shut down.

What is claimed is: 
     
       1. A temperature conditioning system comprising: a supply vessel containing cryogenic vapor and cryogenic liquid, the cryogenic vapor having a cryogenic vapor pressure, the temperature conditioning system utilizing cryogenic liquid evaporation within an evaporation coil, the evaporation coil being ventilated by a vapor powered blower having a vapor inlet connected to receive vapor from said evaporation coil, the system comprising means interconnecting said cryogenic fluid supply and said blower vapor inlet for providing vapor to power said blower independently of said evaporation coil, the system further comprising an excess vapor line flow connecting the interior of the supply vessel to the temperature control system, the excess vapor line including a flow control valve which opens when the cryogenic vapor pressure exceeds a predetermined acceptable value to thereby permit the stored cryogenic vapor to be supplied to the system to thereby reduce the cryogenic vapor pressure to an acceptable pressure value and maintain the system at a positive pressure when the temperature conditioning system is turned off. 
     
     
       2. The temperature conditioning system of claim 1 wherein said interconnecting means provides vapor to said blower vapor inlet at system start-up. 
     
     
       3. The temperature conditioning system as claimed in claim 1, further comprising a cryogenic vapor supply line having a first inlet end located in the supply vessel cryogenic vapor and a second discharge end located outside the supply vessel and whereby cryogenic vapor is supplied to an object of interest. 
     
     
       4. The temperature conditioning system as claimed in claim 1, the system further comprising a first valve and a second valve flow connected to the evaporation coil, a heater flow connected to the first valve and a liquid cryogen outlet line that is flow connected to the first and second valves to selectively supply the liquid cryogen to a heater or the evaporation coil.